Dielectric heating



1955 s. l. RAMBO ET AL 2,723,334

DIELECTRIC HEATING Filed April 14, 1951 Power ,24 supp Fig I 28 28 Charge L I I WITNESSES: INVENTORS Sheldon I. Rambo 8 fl z v gay Bruce Boyd. W 1 ATTORNEY United States Patent DIELECTRIC HEATING Application April 14, 1951, Serial No. 221,616

Claims. (Cl. 21910.77)

Our invention relates to apparatus for the dielectric heat treatment of workpieces, and the power supply sources therefor, and has particular relation to a load circuit for use in such heat treatment.

In accordance with the pertinent apparatus of the prior art, with which we are familiar, every high frequency power supply source has coupled, between its output circuit and the heating electrodes in its load circuit, a fixedcapacity blocking condenser. The latter is used to isolate the direct current anode-voltage supply source from the heating electrodes and the rest of the load circuit. In the practical operation of such blocking condensers, they have proven to be rather vulnerable to damage and costly to maintain in satisfactory operating condition.

In accordance with other apparatus for the prior art, with which we are familiar, for use in particular with workpieces which vary in size, such as is encountered when using a conveyor feed arrangement where workpieces of different sizes are continuously fed to the heating electrodes for heat treatment, it has proven desirable to provide a variable separation between the heating electrodes. This has usually been accomplished by having one electrode move relative to the other, with a flexible conductor means or brush contacts provided to establish an electrical circuit between the high frequency power supply source and the movable electrode, through a blocking condenser.

It is an object of our invention to provide a load circuit for a high frequency power supply source in which the blocking condenser is provided as an integral part of the heating electrode arrangement.

It is a further object of our invention to provide a plate blocking condenser for a high frequency supply generator which is less vulnerable to damage and relatively inexpensive to maintain and keep in satisfactory operating condition.

It is another object of our invention to provide a plate blocking condenser having a fixed capacitance, which is i an integral part of the heating electrode structure, said plate blocking condenser having its constant or fixed capacitance despite position variation of one of the heating electrodes relative to the other heating electrode.

It is a still further object of our invention to provide In accordance with our invention, we provide a pair.

of heating electrodes for the dielectric heat treatment of suitable workpieces. One of the heating electrodes is adjustable in position relative to the position of the other heating electrode, said ad ustable electrode having at least a pair of sides parallel. to .theLfirst heating electrode.

One of said sides, the one furthest in position from the first heating electrode, has an opening therein through which is extended a support member for a third member. The third electrode member is positioned in the space between the pair of sides of the adjustable heating electrode, the support for the third electrode member being electrically conductive and connected to the anode output terminal of a suitable power supply generator.

The work material is positioned between the first heating electrode and the side of the second heating electrode, which is nearest to said first heating electrode, and in addition is opposite the side of the second heating electrode that has an opening therein.

A fixed-capacity plate blocking condenser is provided from the capacitance between the third electrode member and the inner surfaces of the sides of the second heating electrode member, which sidessubstantially surround the third electrode member. As the second heating electrode is moved relative to the first heating electrode and third electrode member, the effective capacitance, between the inner surface of the sides of the second heating electrode and the third electrode member, remains substantially constant. The third electrode member and first heating electrode remain relatively stationary. There is no need for a flexible electrical conductor between the anode terminal of the power supply generator and the movable second heating electrode, since there is a capacity coupling provided in this manner between the third electrode member and the second heating electrode.

The load circuit in accordance with our invention is tuned by means of parallel tuning inductors, which operate in the manner of a short circuited quarter wave length transmission line. Conductive members are pivotally connected to either one or both of the movable second heating electrode and the stationary first heating electrode to make electrical contact thereto. Movement of the adjustable second heating electrode elr'ectively varies the spacing of these conductor members relative to both the first and second heating electrodes. Pigtails, wipers and the like may be used to by-pass the current around the above pivot connections. Variable tuning inductors are provided thereby.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying rawing, in which:

Figure 1 shows an end view of our proposed heating electrode and plate blocking condenser arrangement; and

Fig. 2 shows a perspective view of the apparatus shown in Fig. 1.

In Fig. 1 is shown a pair of heating electrodes 10 and 12 with suitable work material 14 positioned therebetween. For purposes of illustration, the upper heating electrode 12 is shown to be adjustable in position relative to the lower heating electrode It). It is to be understood that either electrode may be made adjustable, even both, if desired. Also, one electrode need not be positioned over and above the other, but may in lieu thereof be positioned to the side of the otherelectrode, or elsewhere. The upper heating electrode 12 has a pair of sides or side members 16 and 18, with side 18 having an opening therein for the extension of a conductive support member 20 holding a third electrode member 22. The third electrode member 22 and the lower heating electrode 10 are stationary relative to each other, with the upper heating electrode 12 being movable relative to both the lower heating electrode 10 and the third electrode member 22. A suitable high frequency power supply source 24, for example of the electronic oscillator type with tubes that have at least cathodes and anodes, is provided. The latter has a first terminal, which may be electrically grounded, and a second terminal which is from the anode circuits of the oscillator tubes and is connected to the conductive support member of the third electrode member 22. The lower heating electrode 16 is connected to the first terminal of the power supply source 24, through the ground connection as illustrated.

In Figure 2 there is shown a perspective view of the heating electrode and plate blocking condenser arrangement, showing the lower heating electrode 10 connected to ground with the upper heating electrode 12 supported for adjustment in position relative to the position of the lower heating electrode 10. Suitable mechanism for such adjustment should be well known to those skilled in the art. The upper heating electrode 12 has a pair of sides 16 and 18, side 18 having an opening therein for the passage of a conductive support member 21) for an inner third electrode member 22.

Also in Figure 2 is shown variable inductance members 26 and 28, which are made of conductive material and are pivotally connected to both the upper heating electrode 12 and the lower heating electrode 10, such that the spacing between conductive members 26 and 28 and respectively the upper heating electrode 12 and the lower heating electrode 11 is variable with the position adjustment of the upper heating electrode 12 relative to the lower heating electrode 111. Conductive members 26 and 28 are chosen in length, and connected to the heating electrodes 10 and 12, such that they each effectively constitute a short circuited transmission line having an inductive reactance at the frequency of operation of the load circuit. Any number of such conductive members may be provided in a similar manner, and located on either side of the workpiece as desired, to provide the desired inductive reactance for effectively tuning the load circuit in accordance with such factors as the spacing between heating electrodes, the size of the workpiece 14 being heat treated, and the size of the heating electrodes.

In the operation of the apparatus shown in Figures 1 and 2, a constant-capacity plate blocking condenser is etiectively provided between the inner third electrode member 22 and the sides 16 and 18 of the upper heating electrode 12. The spacing between the sides 16 and 18 of upper heating electrode 12 is chosen such that the upper heating electrode 12 can be adjusted in posi tion relative to the position of lower heating electrode 10 to accommodate the desired range of work material dimensions. An adequate clearance should always be provided between the third electrode member 22 and either one of sides 16 and 18 of upper heating electrode 12, regardless of the size of the work material being heat treated. The eliective capacitance between the third electrode member 22 and the inner surfaces of the surrounding upper heating electrode 12 provides the constant capacity plate blocking capacitor. The lat ter is employed between the high frequency power supply source 24 and the resonant heating electrode circuit, including heating electrodes 10 and 12 and the tuning inductor members 26 and 28. The resultant plate blocking condenser has a constant capacitance throughout the anticipated variation of upper heating electrode 12 position, because of the unique structural shape of upper heating electrode 12 and the arrangement of its sides 16 and 18 relative to the third electrode member 22. When the upper heating electrode 12 is moved relative to the third electrode member 22, the distance between third electrode member 22 and side 16 changes an amount corresponding to the change in spacing between third electrode member 22 and the other side 18. For example, if the upper heating electrode 12 is raised relative to lower heating electrode 10, the spacing between third electrode member 22 and side 16 decreases and the spacing between third electrode member 22 and side 18 increases. The increase in spacing between third electrode member 22 and side 18 is proportional to the decrease in spacing between third electrode member 22 and side 16. Accordingly, the overall capacitance tween upper heating electrode 12 and third electrode member 22 remains constant throughout the contemplated variation in position of upper heating electrode 12.

As will be apparent from Figure 1 and Figure 2, the anode terminal of the high frequency power supply source 24 is connected through conductive support 20 and third electrode member 22 to the resonant electrode circuit, including the heating electrodes 10 and 12 and tuning inductor members 26 and 28, through an effective capacity coupling such that no direct physical connection is required between the anode terminal of the power supply source and the upper heating electrode 12. This eliminates the need for a flexible conductor member or a sliding connection between the movable upper heating electrode 12 and the anode terminal of the high fre quency power supply source.

The variable inductor members, such as 26 and 28 shown in Figure 2, are provided for the purpose of parallel resonant tuning the electrode circuit, including the heating electrodes 10 and 12. These members are chosen to have a length such that effectively a short circuited quarter wave length transmission line is formed by their pivoted connection to upper heating electrode 12 and their electrical connection to lower heating electrode 10. As the spacing between heating electrodes 10 and 12 is changed, the position and correspondingly the efiective spacing between inductor members 26 and 23 and these electrodes changes to efiectively provide a parallel tuned responant electrode circuit over the desired range of position adjustment of the heating electrodes 10 and 12.

While we have shown and described certain specific embodiments of our invention, many modifications thereof are possible. For example, the upper electrode 12 may be adjustably supported by variable inductance members 26 and 28, or this support can be accomplished in any other manner obvious to those skilled in hte art. Our invention, therefore, is not to be restricted except as is necessitated by the prior art and by the spirit of the appended claims.

We claim as our invention:

1. A first and a second heating electrode, said second heating electrode having a pair of side members which are substantially parallel in position relative to said first electrode, one of said side members having an opening therein, and a third electrode which is positioned between the side members of said second heating electrode.

2. A first and a second heating electrode, said second heating electrode having a pair of side members which are substantially parallel in position relative to said first electrode, one of said side members having an opening therein, and a third electrode being positioned between the pair of side members of said second heating electrode, said third electrode being substantially parallel in position relative to the side members of said second heating electrode.

3. A load circuit for use in the dielectric heat treatment of workpieces comprising, a first and a second heating electrode, said second heating electrode having a pair of side members which are substantially parallel relative to said first electrode, one of said side members having an opening therein, a third electrode member positioned between the pair of side members of said second heating electrode, and a support member for said third ciectrode member, said support member extending through said opening in one of the side members of said second heating electrode.

4. The apparatus of claim 3, characterized by said third electrodemember and said first heatingelectrode being stationary i in position relative to each other.

5. The apparatus of claim 4, characterized by said second heating electrode being movable in position relative to said first heating electrode and said third electrode member.

6. A load circuit for use with a high frequency power supply source in the dielectric heat treatment of workpieces comprising, a first and a second heating electrode, said second heating electrode having a pair of side members which are substantially parallel in position relative to said first heating electrode, one of said sides having an opening therein, a third electrode member, a support for said third electrode member, said support extending through said opening in one side member of said second heating electrode, the other side member of said second heating electrode being positioned nearest to said first heating electrode.

7. The apparatus of claim 6, characterized by said other side member of said second heating electrode and said first heating electrode being adapted to have the workpieces positioned therebetween for purposes of heat treatment thereof.

8. A dielectric heat treatment load circuit for use with a high frequency power supply source having at least an anode and a cathode circuit comprising, a first and a second heating electrode, said second heating electrode having at least a pair of side members which are substantially parallel in position relative to said first heating electrode, a third electrode member positioned between the side members of said second heating electrode, one of the side members of said second heating electrode having an opening therein, a support member for said third electrode member, said support member extending through said opening in one side member of said second heating electrode, said first heating electrode being electrically connected to the cathode circuit of said power supply source and said third electrode member being electrically connected to said anode circuit of said power supply source.

9. A load circuit for use with a high frequency power supply source comprising, a first and a second electrode member, said second electrode member having at least a pair of side members, each of which are substantially parallel in position relative to said first electrode member, said second electrode member being adjustable in position relative to the position of said first electrode member, a conductor member pivotally connected to said second electrode member and extending to electrically contact said first electrode member for all operative positions of said second electrode member throughout its range of adjustment relative to said first electrode member.

10. The apparatus of claim 9, characterized by said conductor member being of such length that it eifectively presents an inductive reactance at the frequency of operation of said load circuit.

References Cited in the file of this patent UNITED STATES PATENTS 1,877,918 Little Sept. 20, 1932 1,880,568 Weir et a1. Oct. 4, 1932 2,059,299 Yolles Nov. 3, 1936 2,147,689 Chaffee Feb. 21, 1939 2,308,043 Bierwirth Jan. 12, 1943 2,467,782 Schuman Apr. 19, 1949 2,494,598 Vahle Jan. 17, 1950 2,504,956 Atwood Apr. 25, 1950 2,504,969 Ellsworth Apr. 25, 1950 2,522,487 Warren Sept. 12, 1950 2,542,702 Prow Feb. 20, 1951 2,583,133 Anderson Jan. 22, 1952 2,586,328 Hagopian Feb. 19, 1952 FOREIGN PATENTS 556,292 Great Britain Sept. 28, 1943 

